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<H1 ALIGN="RIGHT"><A NAME="basics">2 - FLTK Basics</A></H1>
<P>This chapter teaches you the basics of compiling programs
that use FLTK.</P>
<H2>Writing Your First FLTK Program</H2>
<P>All programs must include the file <TT><FL/Fl.H></TT>.
In addition the program must include a header file for each
FLTK class it uses. Listing 1 shows a simple "Hello,
World!" program that uses FLTK to display the window.</P>
<UL>
<P><I>Listing 1 - "hello.cxx"</I>
<PRE>
#include <FL/Fl.H>
#include <FL/Fl_Window.H>
#include <FL/Fl_Box.H>
int main(int argc, char **argv) {
Fl_Window *window = new Fl_Window(300,180);
Fl_Box *box = new Fl_Box(20,40,260,100,"Hello, World!");
box->box(FL_UP_BOX);
box->labelsize(36);
box->labelfont(FL_BOLD+FL_ITALIC);
box->labeltype(FL_SHADOW_LABEL);
window->end();
window->show(argc, argv);
return Fl::run();
}
</PRE></UL>
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<P>After including the required header files, the program then creates a
window:</P>
<UL><PRE>
Fl_Window *window = new <A href="Fl_Window.html#Fl_Window">Fl_Window</A>(300,180);
</PRE></UL>
<P>and a box with the "Hello, World!" string in it:</P>
<UL><PRE>
Fl_Box *box = new <A href="Fl_Box.html#Fl_Box">Fl_Box</A>(20,40,260,100,"Hello, World!");
</PRE></UL>
<P>Next, we set the type of box and the size, font, and style of the label:</P>
<UL><PRE>
box->box(FL_UP_BOX);
box-><A href=Fl_Widget.html#Fl_Widget.labelsize>labelsize</A>(36);
box-><A href=Fl_Widget.html#Fl_Widget.labelfont>labelfont</A>(FL_BOLD+FL_ITALIC);
box-><A href=Fl_Widget.html#Fl_Widget.labeltype>labeltype</A>(FL_SHADOW_LABEL);
</PRE></UL>
<P>Finally, we show the window and enter the FLTK event loop:</P>
<UL><PRE>
window-><A href=Fl_Group.html#Fl_Group.end>end</A>();
window-><A href=Fl_Window.html#Fl_Window.show>show</A>(argc, argv);
return <A href="Fl.html#Fl.run">Fl::run</A>();
</PRE></UL>
<P>The resulting program will display the window in Figure 2-1.
You can quit the program by closing the window or pressing the
<KBD>ESC</KBD>ape key.</P>
<P ALIGN="CENTER"><IMG src="hello.C.gif" alt="Hello, World! Window"><BR>
<I>Figure 2-1: The Hello, World! Window</I></P>
<H3>Creating the Widgets</H3>
<P>The widgets are created using the C++ <TT>new</TT> operator. For
most widgets the arguments to the constructor are:</P>
<UL><PRE>
Fl_Widget(x, y, width, height, label)
</PRE></UL>
<P>The <TT>x</TT> and <TT>y</TT> parameters determine where the
widget or window is placed on the screen. In FLTK the top left
corner of the window or screen is the origin (i.e. x = 0, y =
0) and the units are in pixels.</P>
<P>The <TT>width</TT> and <TT>height</TT> parameters determine
the size of the widget or window in pixels. The maximum widget
size is typically governed by the underlying window system or
hardware.</P>
<P><tt>label</tt> is a pointer to a character string to label
the widget with or <tt>NULL</tt>. If not specified the label
defaults to <tt>NULL</tt>. The label string must be in static
storage such as a string constant because FLTK does not make a
copy of it - it just uses the pointer.</P>
<H3>Get/Set Methods</H3>
<P><tt>box->box(FL_UP_BOX)</tt> sets the type of box the
Fl_Box draws, changing it from the default of
<tt>FL_NO_BOX</tt>, which means that no box is drawn. In our
"Hello, World!" example we use <TT>FL_UP_BOX</TT>,
which means that a raised button border will be drawn around
the widget. You can learn more about boxtypes in
<A href="common.html#boxtypes">Chapter 3</A>.</P>
<P>You could examine the boxtype in by doing
<tt>box->box()</tt>. FLTK uses method name overloading to make
short names for get/set methods. A "set" method is always of
the form "void name(type)", and a "get" method is always
of the form "type name() const".</P>
<H3>Redrawing After Changing Attributes</H3>
<P>Almost all of the set/get pairs are very fast, short inline
functions and thus very efficient. However, <i>the "set" methods
do not call <TT>redraw()</TT></i> - you have to call it
yourself. This greatly reduces code size and execution time. The
only common exceptions are <tt>value()</tt> which calls
<TT>redraw()</TT> and <tt>label()</tt> which calls
<TT>redraw_label()</TT> if necessary.</P>
<H3>Labels</H3>
<P>All widgets support labels. In the case of window widgets,
the label is used for the label in the title bar. Our example
program calls the <A href=Fl_Widget.html#Fl_Widget.labelfont>
<TT>labelfont</TT></A>,
<A href=Fl_Widget.html#Fl_Widget.labelsize><TT> labelsize</TT></A>,
and <A href=Fl_Widget.html#Fl_Widget.labeltype><TT>labeltype</TT></A>
methods.</P>
<P>The <TT>labelfont</TT> method sets the typeface and style
that is used for the label, which for this example we are using
<TT>FL_BOLD</TT> and <TT>FL_ITALIC</TT>. You can also specify
typefaces directly. </P> <P>The <TT>labelsize</TT> method sets
the height of the font in pixels. </P> <P>The <TT>labeltype</TT>
method sets the type of label. FLTK supports normal, embossed,
and shadowed labels internally, and more types can be added as
desired.</P>
<P>A complete list of all label options can be found in
<A href="common.html#labels">Chapter 3</A>.</P>
<H3>Showing the Window</H3>
<P>The <TT>show()</TT> method shows the widget or window. For windows
you can also provide the command-line arguments to allow users to
customize the appearance, size, and position of your windows.</P>
<H3>The Main Event Loop</H3>
<P>All FLTK applications (and most GUI applications in general)
are based on a simple event processing model. User actions such
as mouse movement, button clicks, and keyboard activity generate
events that are sent to an application. The application may then
ignore the events or respond to the user, typically by redrawing
a button in the "down" position, adding the text to an input
field, and so forth.</P>
<P>FLTK also supports idle, timer, and file pseudo-events that
cause a function to be called when they occur. Idle functions
are called when no user input is present and no timers or files
need to be handled - in short, when the application is not doing
anything. Idle callbacks are often used to update a 3D display
or do other background processing.</P>
<P>Timer functions are called after a specific amount of time
has expired. They can be used to pop up a progress dialog after
a certain amount of time or do other things that need to happen
at more-or-less regular intervals. FLTK timers are not 100%
accurate, so they should not be used to measure time intervals,
for example.</P>
<P>File functions are called when data is ready to read or
write, or when an error condition occurs on a file. They are
most often used to monitor network connections (sockets) for
data-driven displays.</P>
<P>FLTK applications must periodically check
(<TT>Fl::check()</TT>) or wait (<TT>Fl::wait()</TT>) for events
or use the <A href="Fl.html#Fl.run"><TT>Fl::run()</TT></A>
method to enter a standard event processing loop. Calling
<TT>Fl::run()</TT> is equivalent to the following code:</P>
<UL><PRE>
while (Fl::wait());
</PRE></UL>
<P><TT>Fl::run()</TT> does not return until all of the windows
under FLTK control are closed by the user or your program.</P>
<H2>Compiling Programs with Standard Compilers</H2>
<P>Under UNIX (and under Microsoft Windows when using the GNU development
tools) you will probably need to tell the compiler where to find the
header files. This is usually done using the <TT>-I</TT> option:</P>
<UL><PRE>
CC -I/usr/local/include ...
gcc -I/usr/local/include ...
</PRE></UL>
<P>The <TT>fltk-config</TT> script included with FLTK can be
used to get the options that are required by your compiler:</P>
<UL><PRE>
CC `fltk-config --cxxflags` ...
</PRE></UL>
<P>Similarly, when linking your application you will need to tell the
compiler to use the FLTK library:</P>
<UL><PRE>
CC ... -L/usr/local/lib -lfltk -lXext -lX11 -lm
gcc ... -L/usr/local/lib -lfltk -lXext -lX11 -lm
</PRE></UL>
<P>Aside from the "fltk" library, there is also a "fltk_forms"
library for the XForms compatibility classes, "fltk_gl" for the
OpenGL and GLUT classes, and "fltk_images" for the image file
classes, <A
HREF="Fl_Help_Dialog.html#Fl_Help_Dialog"><CODE>Fl_Help_Dialog</CODE></A>
widget, and system icon support.
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<TR>
<TD><B>Note:</B>
<P>The libraries are named "fltk.lib", "fltkgl.lib", "fltkforms.lib",
and "fltkimages.lib", respectively under Windows.
</TD>
</TR>
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<P>As before, the <TT>fltk-config</TT> script included with FLTK can be
used to get the options that are required by your linker:</P>
<UL><PRE>
CC ... `fltk-config --ldflags`
</PRE></UL>
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<P>The forms, GL, and images libraries are included with the "--use-foo"
options, as follows:
<UL><PRE>
CC ... `fltk-config --use-forms --ldflags`
CC ... `fltk-config --use-gl --ldflags`
CC ... `fltk-config --use-images --ldflags`
CC ... `fltk-config --use-forms --use-gl --use-images --ldflags`
</PRE></UL>
<P>Finally, you can use the <TT>fltk-config</TT> script to
compile a single source file as a FLTK program:
<UL><PRE>
fltk-config --compile filename.cpp
fltk-config --use-forms --compile filename.cpp
fltk-config --use-gl --compile filename.cpp
fltk-config --use-images --compile filename.cpp
fltk-config --use-forms --use-gl --use-images --compile filename.cpp
</PRE></UL>
<P>Any of these will create an executable named <TT>filename</TT>.
<H2>Compiling Programs with Microsoft Visual C++</H2>
<P>In Visual C++ you will need to tell the compiler where to
find the FLTK header files. This can be done by selecting
"Settings" from the "Project" menu and then
changing the "Preprocessor" settings under the
"C/C++" tab. You will also need to add the FLTK and
WinSock (WSOCK32.LIB) libraries to the "Link"
settings.</P>
<P>You can build your Microsoft Windows applications as Console or
WIN32 applications. If you want to use the standard C <TT>main()</TT>
function as the entry point, FLTK includes a <TT>WinMain()</TT>
function that will call your <TT>main()</TT> function for you.</P>
<P><I>Note: The Visual C++ 5.0 optimizer is known to cause problems with
many programs. We only recommend using the "Favor Small Code"
optimization setting.</I> The Visual C++ 6.0 optimizer seems to be much
better and can be used with the "optimized for speed" setting.</P>
<H2>Naming</H2>
<P>All public symbols in FLTK start with the characters 'F' and 'L':</P>
<UL>
<LI>Functions are either <TT>Fl::foo()</TT> or
<TT>fl_foo()</TT>.</LI>
<LI>Class and type names are capitalized:
<TT>Fl_Foo</TT>.</LI>
<LI><A href="enumerations.html">Constants and
enumerations</A> are uppercase: <TT>FL_FOO</TT>.</LI>
<LI>All header files start with <TT><FL/...></TT>.
</LI>
</UL>
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<H2>Header Files</H2>
<P>The proper way to include FLTK header files is:</P>
<UL><PRE>
#include <FL/Fl_xyz.H>
</PRE></UL>
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<TR>
<TD><B>Note:</B>
<P>Case <I>is</I> significant on many operating systems,
and the C standard uses the forward slash (/) to
separate directories. <i>Do not use any of the following
include lines:</i></P>
<UL><PRE>
#include <FL\Fl_xyz.H>
#include <fl/fl_xyz.h>
#include <Fl/fl_xyz.h>
</PRE></UL>
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